Cellular Senescence and the Future of Equine Osteoarthritis Management

We sit down with Dr. Lynn Pezzanite to explore a promising angle on aging-related equine osteoarthritis (OA): cellular senescence, the pro-inflammatory state where cells release a senescence-associated secretory phenotype (SASP) that can amplify damage inside tissues over time.

We walk through why horses are such a valuable One Health model for osteoarthritis research and why this team compared synovial fluid cells from the joint with peripheral blood mononuclear cells from circulation. Using single-cell RNA sequencing, the study teases apart immune and cellular heterogeneity that bulk methods can blur. One of the most striking takeaways is the compartment split: senescence-associated pathways can be down in peripheral blood yet up in synovial cells, suggesting the joint environment may create a more intense, specialized senescent phenotype.

We also dig into the immune cell story, including why dendritic cells and gamma delta T cells keep showing up as important across both chronic natural OA and early post-traumatic OA work. Then we shift to what this could mean clinically: the promise and cautions around senescence-targeted therapies and the practical case for local intra-articular delivery. Finally, we talk translational hurdles like equine-specific dosing and safety, plus the next research steps to connect senescence burden with OA pain and treatment response.

If you care about equine lameness, osteoarthritis biomarkers, and the future of disease-modifying OA therapy, subscribe, share this with a colleague, and leave us a rating and review wherever you listen.

AJVR article: https://doi.org/10.2460/ajvr.25.09.0343

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Transcript

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Welcome And The Research Question

Lisa Fortier 0:31

Welcome to Epic Award-winning Veterinary Vertex, the Avium Made Journal's podcast where we delve into behind-the-scenes look with manuscript authors. I'm editor in Chief Lisa Fortier, joined by associate editor Sarah Wright. Today we're discussing how senescent associated gene pathways are differentially expressed in equine aging-related OA or osteoarthritis with our fabulous guest, my friend and colleague Lynn Pezzanate. Thank you for joining us, Lynn.

Sarah Wright 0:58

Thanks so much for having me today. So, Lynn, for our listeners, what is cellular senescence?

Cellular Senescence Explained Simply

SPEAKER_02 1:04

Cellular senescence is an aging-associated condition where cells secrete a senescence-associated secretory phenotype, which induces inflammation and senescence in the cells around them. It's associated with multiple aging-related conditions, including muscoskeletal diseases like osteoarthritis.

Lisa Fortier 1:25

Lynn, what motivated you to investigate this? You've had a lot of really cool parallel paths. And why do you think this is an important question to pursue, particularly in the line of OA?

SPEAKER_02 1:36

Yeah, it's a great question. Osteoarthritis continues to be one of the most common muscoskeletal conditions diagnosed in horses. It limits quality of life and athletic performance. And similarly, the worldwide incidence of OA in people is increasing concurrently and anticipated to continue to increase with a globally aging population. So several challenges we continue to face in treating OA across species include that early diagnostic

Why OA Needs Better Biomarkers

SPEAKER_02 2:05

biomarkers remain limited, and our commonly applied imaging modalities such as radiographs or x-rays don't necessarily correlate to clinical pain. And they particularly lack sensitivity in those early stages of disease. So the rising prevalence of OA in an increasingly aging population, and the honestly somewhat alarming fact that all of our current treatment options across species remain palliative, I think, highlight the need for an improved understanding, continued improved understanding of OA pathogenesis and development of earlier both diagnostic biomarkers and disease-modifying interventions. And so that prompted us to explore senescence as potentially one pathway to address both of those questions, earlier biomarkers and interventions, particularly in aging associated OA.

Sarah Wright 2:57

So, Lynn, did you enter the study with a specific hypothesis about how senescence might differ locally within the joint versus systemically?

SPEAKER_02 3:07

We did hypothesize that the transcript genomic signatures would be differentially expressed between sites with the joint environment in a way likely exhibiting a more intense upregulation of senescence signatures. And that's based on some data in the human literature that's concurrently looking at this too. But that was our hypothesis going in.

Why Horses Model Human OA

Lisa Fortier 3:28

Tell the listeners, Lynn, why our favorite veterinary patient, the horse, is such a valuable model for studying aging-associated OA.

SPEAKER_02 3:37

Horses really represent an excellent model to study OA through a one-health lens. They're athletes and they develop OA at a relatively high rate. In the US, estimates up to one-third of horses overall have some degree of OA. And between 50 to 80% of geriatric horses, so those over 15 to 20 years of age develop OA like humans. They naturally age longer than most companion animal species living into their 20s and 30s. And so in that sense, they also represent an excellent model for human OA, as well as similarities in cartilage thickness, articular loading forces, and joint volume. And so while our goal is first to advance equine health with this work, I'd emphasize that overall we were really trying to take a one-health approach to also identify potential commonalities in OA disease processes across species as a strategy that may potentially enable more robust biomarker identification and therapeutic development.

Sarah Wright 4:40

Very

Study Design And Single-Cell RNA-Seq

Sarah Wright 4:41

cool. So your study compared senescence signatures in synovial fluid cells and peripheral blood mononuclear cells. What was the rationale for examining both compartments simultaneously?

SPEAKER_02 4:53

Yeah, so while we hypothesized that the compartments would likely differ in senescent cell expression, we wanted to evaluate both concurrently to determine if there were potential biomarkers in circulation that also correlated to the joint landscape and that could be more easily sampled for future biomarker development than synoviosynthesis of the joint.

Lisa Fortier 5:16

Sticking with methodology, uh, why did you choose single-cell RNA-seq to reveal these patterns compared to bulk transcriptomics?

SPEAKER_02 5:26

The integration of single-cell RNA sequencing and kind of our advancement of this technology in the equine field was, I think, really critical here to offer an approach that overall deconvolutes the cellular heterogeneity and the immune complexity of disease tissues such as osteoarthritic joints that would otherwise just be missed kind of in the overall differential gene expression and pathway analyses that are generated by bulk transcriptonics.

Sarah Wright 5:54

So your custom gene set incorporated more than 3,000 genes curated from published metadata. Can you walk us through how that gene set was developed and validated?

SPEAKER_02 6:03

The senescence gene set we developed, and I do want to credit Linda Chow, our research scientist, and two awesome PhD students, Dylan Amons and Jacob Singer, who worked on this project. So I can't take credit for that. But the way that was developed was by combining authoritative databases that included gen age and cell age, as well as four published historical human data sets that defined senescence gene signatures. And then we mapped those to equine orthologs using the ensemble gene 115 program.

Joint Versus Blood Senescence Signals

Lisa Fortier 6:40

Lynn, you spoke a little bit earlier about uh why you chose peripheral blood mononuclear cells and synovial cells. And interestingly, one of the really cool findings amongst the many in your manuscript was this uh pathways were downregulated in peripheral blood and upregulated in synovial cells. How might we go about interpreting that disconnect?

SPEAKER_02 7:01

Yeah, um, this is something we spent a while discussing, but I think to briefly summarize, I would interpret it to suggest that while senescence is a systemic process associated with aging, the joint environment in a way induces a specialized, more pronounced senescent phenotype that likely continues to perpetuate that local tissue destruction in progression. And I think importantly, again, some of the recent work across species in humans also supports that, that um there's it's different in circulation versus in the joint, which I think maybe as we move into the next portion on clinical application of this points to a more targeted local approach, potentially.

Sarah Wright 7:45

So, Len, the single-cell RNA sequencing data highlighted cell type-specific heterogeneity and senescence expression. Which cell populations emerged as the most biologically relevant or surprising to you?

SPEAKER_02 7:59

The dendritic and the gamma delta T cell populations emerged as potentially most biologically relevant, as our um our one previous publication using single cell sequencing and chronic equine OA indicated both of those were upregulated in natural OA. And then we followed that up recently with um looking at early PTOA in horses and also identified gamma-delta T cells as a potentially early biomarker. Um trying to understand better the correlation of some of um these upregulated immune lineages and senescence expression is kind of some next steps for this work.

Lisa Fortier 8:38

Yeah, the T cells are highly underinvestigated. We've had a couple stabs at it too, and there's a lot to learn. They're not easy to do, those studies, uh, trying to isolate the T cells enough of them to do a study. So well done. What role do you think the gamma delta and other T cells and immune populations play in OA progression?

SPEAKER_02 8:57

Yeah. Um, and so I think I think an important point here is we'll be tailoring um disease treatments better to stage of disease to target specific immune cell lineages. So our previous study, um, and again, that was our prior grad student, Dylan Amon's work, um, applying single-cell RNA sequencing techniques to synovial fluid and synovium samples from horses with very chronic natural OA. So, in that case, horses undergoing arthroscopy but had documented disease for several years at least, highlighted, again, the gamma delta T cells and myeloid cells, which include macrophages and dendritic cells, to be overexpressed in OA joints. And then we since expanded on that with our Grace and Jockey Club funded study, where we followed horses with cartilage injury in the very early stages, so the first 18 weeks of OA progression following joint injury, to determine primarily which immune populations were impacted, again, using these unbiased single-cell sequencing approaches. And we again found that the gamma delta T cells were some of the most impacted early on in OA progression. So I think our findings to date support the T cells are important, but the different immune populations are enriched and likely playing a role at different stages of progression, which is something we hope to explore further longitudinally, and particularly in the context of when senescence cell profiles are upregulated in the disease course.

Sarah Wright 10:32

Sounds like a lot of future research coming from you. Hopefully, we'll see that too in our journals. So the senescence-associated secretory phenotype appeared particularly enriched in cycling cells. Do you think these cells represent a particularly important therapeutic target?

SPEAKER_02 10:47

Yeah, it's a great question and one that I think we have to interpret cautiously. So the on single-cell RNA-seq, the cycling cell population represents or is referring to multiple cell populations of cells that are actively undergoing either division or DNA replication or preparation for mitosis. And so, in the context of a WA, that could likely include activated immune cells such as T or B cells or macrophages undergoing expansion in response to inflammation, for example. So, yes, I think they could represent a therapeutic target, but we need to better understand and kind of look into that heterogeneous population further to better define their phenotype overall in the context of OA and understand um better their role before we can target them specifically.

Senotherapeutics Translational Hurdles Next Steps

Lisa Fortier 11:38

How do you envision uh xenotherapeutics fitting into the future of equine OA management? Do you see promise in the senolytics, xenomorphics, or another approach entirely to address this?

SPEAKER_02 11:50

I think the data do support further investigation of xenotherapeutics as part of a multimodal approach to OA management. Um, and that'll kind of get into our next steps and ongoing areas. Um, I think potentially xenolytics such as metformin and quercetin could potentially have a more potent effect to directly address aspects of aging, while xenomorphics may be more beneficial to manage aspects of chronic aging-associated inflammation with potentially lower risk of off-target toxicity compared to senolytics with long-term administration. Um, all of this, I think, needs to be worked out in horses specifically, but um, I do see a potential role in addition to other potentially more potent interarticular injections or long-term management strategies like weight loss and rehabilitation. Um and so that's definitely something I want to explore further. But I don't I don't see the potency, and I don't, you know, my knowledge of the human studies don't indicate the potency like some other interarticular treatments like corticosteroids, for example, to immediately provide symptom relief. But I do see a potential role with uh long-term management of a way and associated comorbidities with OA.

Sarah Wright 13:07

What are the major translational hurdles that need to be addressed before senescence-targeted therapies could realistically enter clinical equine practice?

SPEAKER_02 13:17

Yeah, that's a great question. I think the immediate translational hurdles to entering practice include further studies on pharmacokinetics and dynamics to determine dosing and route of administration while minimizing off-target adverse side effects. Um, one potential way I believe we could address this in our equine patients, which is um, I believe supported by the data we discussed today, would be local interarticular delivery rather than systemic administration, how they're frequently used in people. Um, and that strategy, I think, would also make extrapolation of dosing to horses more affordable for our clients. But all of that are things we need to look at specifically in horses.

Lisa Fortier 13:57

So lots to look at, Lynn. But and looking ahead, what are the major, the really big ones, uh, research quests that questions that your group are most interested in following, following up with this study?

SPEAKER_02 14:08

Yeah, so um, in the current follow-up work, um, we've been screening phenotherapeutics in an in vitra model of senescence in equine synobi sites using um complementary phenotypic and transcriptomic approaches to determine and down-select the optimal equine treatments. And then in our next steps, we'll be moving into in vivo-dosing studies with the goal generally to optimize delivery strategies in OA. And then, as a second overall goal, um, I'd like to better understand the role of senescence burden in OA pain and potentially prediction of response to therapy in horses with natural OA. And there's some really interesting, uh really recent work in human literature correlating senescence burden to um pain status or self-reported pain. So I'd be interested to see if we could detect similar differences in our equine patients.

Sarah Wright 15:02

Wow, how cool. I learned a lot today, and it sounds super exciting. So I can't wait to see more work come out too about this. But for now, Lynn, thank you so much for joining us and for serving on our scientific reboard for Jabmon AJBR. We really appreciate your time. Thanks so much for having me. And for our listeners and viewers, you can read Lynn's article on AJBR. I'm Sarah Wright here with Lisa Fortier. Be sure to tune in next week for another episode of Veterinary Vertex. And don't forget to leave us a rating and review on Epha Podcast or wherever you listen.